Thinking skills may suffer on hot days

(Reuters Health) - Heat waves can sap productivity by slowing down thinking, even in the young and healthy, a small study suggests.

Harvard researchers found that during a summer heat wave, students living in dorms without air conditioning consistently scored lower on daily cognitive tests over the course of nearly a week than students in buildings with AC.

“For the first time, we’ve been able to find a detrimental effect of heat waves in young healthy adults,” said lead author Jose Guillermo Cedeno Laurent, a research fellow and associate director of the Healthy Buildings Program at the Harvard T. H. Chan School of Public Health in Boston.

“Among that group (who had no AC) there were longer reaction times and lower accuracy compared to an identical group of students who lived with air conditioning,” he told Reuters Health in an email.

The researchers followed 44 undergraduate and graduate students in their late teens and early 20s for 12 consecutive days during July of 2016. Twenty-four of the students resided in buildings constructed in the 1990s that were equipped with central air conditioning, while 20 lived in Neo-Georgian-style low-rise brick buildings built between 1930 and 1950 with no cooling system.

The researchers designed their experiment so that the 12 days included a five-day heat wave, preceded by five days with more moderate temperatures, and followed by two days of cooler weather. Temperatures inside the building without air conditioning averaged 26.3 degrees Celsius (79.3 degrees Fahrenheit) and ranged as high as 30.4 degrees C (86.7 F).

Average temperatures in the air-conditioned buildings were 21.4 degrees C (70.5 F), ranging up to 25 degrees C (77 F).

Each morning the students took two tests of cognition on their smartphones. One test, which required students to correctly identify the color of displayed words, measured their reaction speed and ability to concentrate and block out distractions. The other test, which presented basic arithmetic problems, measured mental quickness and working memory.

During the heat wave, students in buildings with no cooling had 13.4 percent slower reaction times on the color-word tests and 13.3 percent lower scores on the math tests, compared to those living in dorms with air conditioning.

Much previous research on the effects of extremely hot weather has been in vulnerable populations that are at risk of dying: either the very young or the very old, the study authors note in PLOS Medicine.

“This study looks at the effects of heat in a population we all think of as generally being resilient,” said study coauthor Joe Allen, co-director of Center for Climate, Health and the Global Environment at the Harvard T. H. Chan School of Public Health.

And while much media coverage has been on people dying prematurely, “the fact is, millions are impacted by heat waves,” Allen said. “And with climate change, and the increased duration of heat waves, we’re going to see an increased impact on performance and learning.”

The new study “is adding to a very quickly growing literature on the effects of heat exposure on student outcomes,” said Jisung Park, an assistant professor of environmental health sciences at the Fielding School of Public Health at the University of California, Los Angeles. “It’s very consistent with other studies showing that hot temperatures, whether at home or in the classroom, can have a detrimental effect on learning.”

No one knows exactly why we don’t seem to be as smart when we’re hot. But it may be that the body is pulling blood away from certain parts of the brain as it tries to cool itself down, said Park, who wasn’t involved in the current study.

“Of course, the elephant in the room is that heat waves are going to be much more frequent,” Park said. “While a 2 degree increase in average temperature may not sound like much, an additional 30 days of temperatures above 95 degrees each year may sound more urgent.”